1. Field of the Invention
The present invention relates to a cap which is to be attached to a container main body holding a liquid which contains a surface active agent and which is excellent in effect of ESCR (ENVIRONMENTAL STRESS CRACKING RESISTANCE).
2. Description of the Related Art
Liquid containing a surface active agent such as detergent is held in a bottled container made of resin. A cap attached to a port neck part of the container main body is detached, and then the content liquid is used while properly measuring the quantity by the detached cap. After the use of the content liquid, the cap is attached for closing to the port neck part again. In the bottle container of the type as just mentioned, during repetition of the attaching and detaching operation of the cap and/or by measuring the content liquid with the cap, the liquid adheres to the cap. Then, under the adverse effect of the surface active agent and also under the adverse effect of the repeated stress at the time of attaching and detaching operation, the cap is susceptible to get broken by environmental stress crack. Moreover, in case the content liquid is a liquid containing a surface active agent and sodium hypochlorite, the cap more easily gets broken by environmental stress crack, due to synergetic effect of the surface active agent and sodium hypochlorite.
The breakage of the cap due to environmental stress crack is liable to occur by crack which occurs at a specific part of the cap to which the content liquid adheres and a stress is concentratedly applied, such as a joint part between a top surface part and a peripheral wall part or a terminal part on the top surface side of a female thread. According to the conventional related art, it is attempted to prevent the cap from getting broken by increasing the thickness of the such specific part for reinforcement. However, there are such inconveniences that the quantity of resin as the material of the cap is increased and the time for plasticizing and for cooling in a production process such as an injection molding is increased to thereby decrease productivity.
It is an object of the present invention to provide a cap capable of effectively preventing breakage of the cap caused by the environmental stress crack, without a need of increasing the thickness of the cap.